Means for supporting an impeller of a centrifugal compressor

ABSTRACT

In a centrifugal compressor, a rotatable shaft has conically tapered portions and an impeller and a front vane are mounted, as separate components, on the tapered portions of the shaft. A first buffer member or spring is interposed between a retaining member and the inlet end of the front vane assembly. A second buffer member or spring is interposed between the vane assembly and the impeller. The buffer members may be in the form of conical springs. The first buffer member is substantially stronger than the second buffer member, and both buffer members act in the same direction to bias the vane and the impeller to the respective tapered portions of the shaft to prevent radial gaps between the vane and the shaft and between the impeller and the shaft.

United States Patent [54] MEANS FOR SUPPORTING AN IMPELLER OF A CENTRIFUGAL COMPRESSOR t 5 Claims, 6 Drawing Figs.

[52] U.S. Cl 416/183, 416/185, 416/188, 416/244 [51] Int. Cl F01d 5/04 [50] Field ofSearch 416/198,

[56] References Cited UNITED STATES PATENTS 1,472,077 10/1923 Lockwood Primary Examiner-Everette A. Powell, Jr. Attorney-McGlew and Toren ABSTRACT: ln a centrifugal compressor, a rotatable shaft has conically tapered portions and an impeller and a front vane are mounted, as separate components, on the tapered portions of the shaft. A first buffer member or spring is interposed between a retaining member and the inlet end of the front vane assembly. A second bufier member or spring is interposed between the vane assembly and the impeller. The buffer members may be in the form of conical springs. The first buffer member is substantially stronger than the second buffer member, and both buffer members act in the same direction to bias the vane and the impeller to the respective tapered portions of the shaft to prevent radial gaps between the vane and the shaft and between the impeller and the shaft.

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INVENT OR \Ti r o NOmurQ ATTORNEY 3 MEANS FOR SUPPORTING AN IMPELLER OF A CENTRIFUGAL COMPRESSOR BACKGROUND OF THE PRIOR ART Generally speaking, in rotating machinery, such as compressors or the like, the center of gravity of the body of revolution should be as closely as possible at the axis of the shaft. If the weight is designated by W, the angular velocity by N, and the eccentric arm between the centers of the shaft and of gravity by S, the amount of unbalanced force or effort caused by the eccentricity is proportional to W, N and S. If the unbalanced efi'ort is thereby increased, not only is the body of revolution incapable of smooth rotation, but also burning out of the supporting bearings for the body will occur.

It follows that, in the case of a high-speed rotating body, the eccentric arm S must not be large, because of the deformations due to its centrifugal force and the heat, not only in the stationary state but in the rotating state. On the contrary, in the conventional centrifugal compressor in which the front vane and the impeller are formed integrally with each other, the production of a larger eccentric arm S in the supporting device may be avoided, but only small centrifugal compressors have such an integrally formed front vane and impeller. In all except the smaller size centrifugal compressors, the vane and the impeller comprise separate components and it may be impossible to avoid occurrence of a larger eccentric arm S with the conventional means for supporting the impeller on the shaft.

FIGS. 1, 2 and 3 illustrate a conventional means for supporting the impeller of a centrifugal compressor on the shaft and as a component which is separate from the vane which is also supported on the shaft. In these figures, a shaft 01 is rotated by suitable driving means which have not been shown. An impeller 02 is secured on a tapered portion of shaft 01 by means of a key 03. Front vanes are also engaged with the tapered portion of shaft 01, in a manner similar to the engagement of impeller 02 therewith, and are connected, by means of knock pin 05 to rotate with impeller 02. These vanes receive gaseous fluid from an inlet, as shown by an arrow, and radially accelerate the gaseous fluid to pressurize the latter while delivering it to an outlet. Such pressurizing is effected by rotation of front vane 04 and impeller 02 as a unit with shaft 01.

A nut 06 is screwed on to a threaded portion of shaft 01 and, through a spring 07, urges front vane 04 and impeller 02 axially along the tapered portions of shaft 01. An inner vortex chamber 08 is provided adjacent front vane 04 and impeller 02.

With the just described conventional means for supporting an impeller of a centrifugal compressor on a shaft, it is very difficult, from the standpoint of workability, to engage both impeller 02 and front vane 04 with tapered portions of shaft 01 at the same time even in a stationary state of the parts. Furthermore, even though the front vane 04 and the impeller 02 could be firmly engaged with the tapered portion of the shaft 01 while the parts are stationary, once the parts are rotated, the resultant elongation in a radial direction, due to the centrifugal force and heat, results in a differential expansion of the two parts 02 and 04, thus causing a gap in the radial direction between the shaft and the two parts.

FIG. 2 illustrates the case in which the front vane 04 is maintained in contact with the tapered portion of shaft 01 by the resultant force OF of spring 07. The force OF of spring 07 does not act on impeller 02, which elongates, in the amount 08, in a radial direction because of deformation due to centrifugal force and heat. Impeller 02 thus has a vibrating state in relation to shaft 01 so that the maximum radial gap on one side becomes 2-08. Thus, the maximum eccentricity arm of the center of gravity of impeller 02 is 08. Additionally, impeller 02, in such case, moves axially in the amount of 08as the maximum displacement resulting from the production of a radial gap. With respect to this axial displacement, if the tapered portion has a ratio of ml for the length n, in the radial direction, 08is equal to the product of the length n08, or 08= "-08, and impeller 02 fluctuates.

FIG. 3 illustrates the case in which, during rotation, impeller 02 is firmly in contact with the tapered portion of shaft 01 by means of the force OF of spring 07. In this case, even with an increased force OF of spring 07 acting on front vane 04, axial movement of front vane 04 along the tapered portion of shaft (ll is prevented, so that front vane 04 elongates radially in the amount 08due to heat deformation and other defects, and vibrates to the extent that it reaches a maximum radial gap 208with respect to one side and shaft 01. Thereby, the maximum eccentric arm of the center of gravity of front vane 04 is 05. It follows, of course, that front vane 04 does not fluctuate axially inasmuch as this vane is urged in the axial direction of impeller 02 by means of the force OF of spring 07.

As previously stated, if the center of gravity of front vane or vanes 04 and impeller 02 is eccentric to the axis of shaft 01 so that there occur vibrating phenomena and unbalanced forces during rotation, the eccentricity increases with the result that it lowers the efficiency of the compressor in addition to introducing defects and burning of the bearing and other components. Furthermore, the operational noise is increased.

SUMMARY OF THE INVENTION This invention relates to means for supporting an impeller of a centrifugal compressor on a shaft and, more particularly, to an improved supporting means supporting an impeller and an associated front vane, formed as separate components, on tapered portions of a shaft.

The present invention eliminates the above-mentioned disadvantages of conventional supporting means for an impeller of the type in which the front vane and the impeller form separate components of a centrifugal compressor. The invention furthermore provides a supporting means by means of which the center of gravity of the front vane and the impeller are prevented from increasing eccentricity not only in the stationary state but also in the rotating statel In accordance with the invention, in a centrifugal compressor in which an impeller and a front vane or vanes are mounted, as two separate components, on tapered portions of the compressor shaft, a first buffer member or spring is provided at the inlet side of the front vane. A second buffer member is provided between the front vane and the impeller. The two bufier members are so related that the first buffer member is stronger than the second buffer member. The two buffer members act in the same axial direction so that they urge the front vane and the impeller along the conically tapered portions of the shaft, thereby preventing production of a gap between the front vane and the impeller and the contacting portions of the shaft.

In accordance with the present invention, the front vane and the impeller are always urged by the buffer members, irrespective of whether the parts are stationary or rotating, so that they are maintained in contact with the tapered portions of the shaft to prevent excessive eccentricity of the center of gravity and to provide a smooth rotary motion.

An object of the present invention is to provide an improved 'means for mounting an impeller and a front vane or vanes, the

impeller and the front vane or vanes comprising separate components, on tapered portions of a shaft of a centrifugal compressor.

Another object of the invention is to provide such a mounting means by means of which both the front vane and the impeller are maintained in firm contact with the respective tapered portions of shaft.

A further object of the invention is to provide such a mounting means including a first buffer engaged between a retaining member and the inlet end of the front vane, and a second buffer engaged between the front vane and the impeller.

Another object of the invention is to provide such a mounting means in which the first b'ufier or buffer member is stronger than the second buffer or buffer member.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawings:

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a diametric sectional view through a centrifugal compressor illustrating prior art mounting means;

FIGS. 2 and 3 are partial radial sectional views through the centrifugal compressor shown in FIG. 1 and illustrating certain effects occurring during operation;

FIG. 4 is a diametric sectional view through a centrifugal compressor embodying the mounting means of the present invention; and

FIGS. 5 and 6 are partial radial sectional views illustrating certain effects occurring during operation of the compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENT The prior art arrangement shown in FIGS. 1, 2 and 3 has previously been described.

Referring now to FIG. 4, a shaft 1 of a centrifugal compressor has an impeller 2 mounted thereon and secured to rotate therewith through the medium of a key member 3. Impeller 2 is engaged with a cylindrical portion la of shaft 1 and also with a conically tapered portion lb of shaft 1. A front vane or vanes 4 are also mounted on shaft 1 and secured to rotate therewith through the medium of a key member 5. The vane 4 or vane assembly is mounted on a conically tapered portion lc of shaft 1. Thus, both impeller 2 and vane assembly 4 rotate, as a unit with shaft 1, within an inner vortex chamber 6 so that gaseous fluid is drawn in at an inlet of vortex chamber 6 and delivered radially outwardly from an outlet, the gaseous fluid being thereby pressurized.

A nut 7 is screwed on to a threaded portion 1d of shaft 1, and a first spring 8 is provided between nut 7 and front vane assembly 4 to bias vane assembly 4 and impeller 2 axially to the right. A second spring 9 is provided between front vane assembly 4 and impeller 2, which are engaged, respectively, with conically tapered portions 1c and lb of shaft 1.

In the arrangement just described, a gap c which is somewhat larger than that of a conventional compressor of this type, including separate impeller 2 and vane assembly, 4 is provided between the adjacent surfaces of vane assembly 4 and impeller 2. The buffer action of the second spring 9, which means the amount of the action during compression and tension, is weaker than that of the spring 8. In addition, although impeller 2 is illustrated as engaged with a cylindrical portion la and a conically tapered portion lb of shaft 1, it may be engaged solely with a conically tapered portion.

Nut 7 is screwed on to shaft 1 sufiiciently tightly so as to resist the buffered action in any state of the first and second springs 8 and 9. If the buffer force 4F of the first spring 8 is twice that 2F, of the second spring 9, front vane assembly 4 and impeller 2 are urged, by means of the first and second springs 8 and 9, to the right along the conically tapered portions 10 and lb in contact with shaft 1, so as to be firmly engaged therewith not only in the stationary state but also in the rotary state.

Referring now to FIGS. 5 and 6, which illustrate the supporting state of vane assembly 4 and impeller 2 during rotation, FIG. 5 denotes the case that, notwithstanding front vane assembly 4 is engaged in contact with conically tapered portion lc of shaft 1, during rotation a gap 8 is produced in the radial direction, by means of centrifugal force, this gap appearing between the impeller 2 and shaft 1. Furthermore, there is an axial displacement of impeller 2 through a distance n6 due to the occurrence of gap 8, where n is a length in the axial direction and when the taper of the conically tapered portion lb has a ratio of ml. In this case, the second spring 9 will act at the starting point of the spring contacting position of front vane assembly 4 first engaged in in contact therewith, and impeller 2 is positively engaged in contact with shaft 1 so that it is firmly supported thereby. Thus, impeller 2 is-biased by means of a bufi'er force 2F in the direction of the arrow and at the conically tapered portion lb of shaft 1.

FIG. 6 illustrates a case which is the contrary of that shown in FIG. 5 in that, notwithstanding that impeller 2 is firmly in contact with shaft 1, during rotation a gap 6 caused by heat deformation and the like, in the radial direction, and a displacement of n6' in the axial direction, are produced, where n is a length in the axial direction and when the taper of the conically tapered portion 10 has a ratio of n'zl. In this case, since the buffer force 4F of the first spring 8 is twice the buffer force 2F of the second spring 9, the first spring 8 will act on front vane assembly 4 so that the latter is firmly engaged in contact with the conically tapered portion 10 of shaft 1, with the second spring 9 being compressed. Thus, both the first and second springs 8 and 9 are effective in the direction of the arrow to maintain the first engagement of the impeller and the front vane assembly with the respective conically tapered portions of shaft 1.

Thus, even though front vane assembly 4 and impeller 2 are divided into two separate components, the unbalanced force, during rotation, is eliminated, inasmuch as the center of gravity of front vane assembly 4 and impeller 2 coincides with the axis of shaft 1 as the vane assembly and the impeller are always firmly engaged in contact with the respective tapered portions of shaft 1, not only in the stationary state but also in the rotating state. Consequently, the centrifugal compressor rotates with smooth operation of front vane assembly 4 and impeller 2, so that there is no deleterious effect on the bearings or burning of the bearings or other components, resulting in long life for the parts. From the foregoing detailed description of the preferred embodiment of the invention, it will be clear that the mounting arrangement of the present invention positively supports a body of revolution without any eccentric movement of the center of gravity, even during rotation of a rotor of a centrifugal compressor in which the impeller and a front vane assembly form separate components. Summarizing, the mounting arrangement comprises a first buffer member or spring at the inlet side of the front vane assembly, and a second buffer member or spring between the front vane assembly and the impeller. The first buffer member is substantially stronger than the second buffer member, with respect to its biasing force, and both buffer members act in the same axial direction to urge the front vane assembly and the impeller into firm engagement with the respective conically tapered portions of the centrifugal compressor shaft. Thereby, these buffer members prevent the production of a gap between the shaft, on the one hand, and the front vane assembly and the impeller. on the other hand.

What is claimed is:

1. In a centrifugal compressor including a rotatable shaft having conically tapered portions and an impeller and a front vane assembly mounted, as separate components, on the tapered portions of the shaft, an impeller and vane assembly mounting arrangement comprising, in combination, a retaining member secured to said shaft adjacent the inlet end of said front vane assembly; a first buffer member embracing said shaft between said retaining member and said front vane assembly; and a second buffer member embracing said shaft between said front vane assembly and said impeller; said buffer members acting in the same axial direction to bias a front vane assembly and said impeller, onto the respective tapered portions of the shaft, to prevent radial gaps between said front vane assembly and said shaft and between said impeller and said shaft during rotation of said shaft.

2. In a centrifugal compressor, an impeller and vane assembly mounting arrangement. as claimed in claim 1, in which said first and second buffer members comprise springs embracing said shaft.

3. In a centrifugal compressor, an impeller and vane assembly mounting arrangement, as claimed in claim 2, in which the effective force of said first buffer member is greater than the efiective force of said second buffer member, in the same axial direction.

5. In a centrifugal compressor, an impeller and vane assembly mounting arrangement, as claimed in claim 4, in which said impeller and said vane assembly are mounted on said shaft with an initial small axial gap therebetween. 

1. In a centrifugal compressor including a rotatable shaft having conically tapered portions and an impeller and a front vane assembly mounted, as separate components, on the tapered portions of the shaft, an impeller and vane assembly mounting arrangement comprising, in combination, a retaining member secured to said shaft adjacent the inlet end of said front vane assembly; a first buffer member embracing said shaft between said retaining member and said front vane assembly; and a second buffer member embracing said shaft between said front vane assembly and said impeller; said buffer members acting in the same axial direction to bias a front vane assembly and said impeller, onto the respective tapered portions of the shaft, to prevent radial gaps between said front vane assembly and said shaft and between said impeller and said shaft during rotation of said shaft.
 2. In a centrifugal compressor, an impeller and vane assembly mounting arrangement, as claimed in claim 1, in which said first and second buffer members comprise springs embracing said shaft.
 3. In a centrifugal compressor, an impeller and vane assembly mounting arrangement, as claimed in claim 2, in which the effective force of said first buffer member is greater than the effective force of said second buffer member, in the same axial direction.
 4. In a centrifugal compressor, an impeller and vane assembly mounting arrangement, as claimed in claim 3, in which the effective force of said first buffer member is substantially twice the effective force of said second buffer member, in the same axial direction.
 5. In a centrifugal compressor, an impeller and vane assembly mounting arrangement, as claimed in claim 4, in which said impeller and said vane assembly are mounted on said shaft with an initial small axial gap therebetween. 